This invention relates to a fluid control valve, and more particularly to a fluid control valve suitable for use for a construction equipment.
A valve mechanism or apparatus which has been conventionally used for controlling an arm cylinder and a boom cylinder of a construction equipment is generally constructed in such a manner as shown in FIG. 1. More particularly, the conventional valve mechanism or apparatus includes a neutral passage 1, to which a control valve 2 for a boom cylinder and a control valve 3 for controlling an arm cylinder are connected. When the control valve 2 for controlling the boom cylinder is changed over to supply pressure oil to the boom cylinder, it closes the neutral passage 1.
The control valve 3 for controlling the arm cylinder includes a spool 4 having one end facing a spring chamber 5 and the other end facing a pilot chamber 6. When any pressure is not applied to the pilot chamber 6, the spool 4 is kept at a position shown in FIG. 1 by means of a spring 7 arranged in the spring chamber 5, to thereby communicate the neutral passage 1 with a tank 8. An actuator passage 9 communicating with the arm cylinder constantly communicates with the neutral passage 1 irrespective of a moved position of the spool 4. Application of a pilot pressure to the pilot chamber 6 in this state causes the spring 4 to be moved against the spring 7, resulting in communication between the neutral passage 1 and the tank 8 being blocked. The actuator passage 9 is provided with a load check valve 10.
Reference numeral 11 designates a change-over valve provided separate from the control valves 2 and 3, which serves to operate a parallel passage 12. The change-over valve 11 includes a spool 13 which is so arranged that one end thereof faces a spring chamber 14 and the other end thereof faces a pilot chamber 15. The spring chamber 14 is provided therein with a spring 16, which acts to cause the parallel passage 12 to communicate through a first oil communication hole 17, a communication hole 18, a second oil communication hole 19 and a load check valve 20 to the actuator passage 9 when the spool 13 is at a normal position shown in FIG. 1.
The spring chamber 14 is arranged so as to communicate through an orifice 21 to the parallel passage 12, and the orifice 21 is connected on a downstream side thereof through an on-off valve 22 to a tank 23. Also, the pilot chamber 15 communicates with the parallel passage 12.
In the conventional mechanism or apparatus constructed as described above, when it is not desired to actuate the boom cylinder, the control valve 2 is kept at its neutral position, so that the neutral passage 1 is kept open. This results in fluid supplied to the neutral passage 1 flowing to the control valve 3. At this time, when the control valve 3 is kept at a normal position shown in Fig. 1, the fluid flowing into the control valve 3 is returned to the tank 8. Accordingly, when a pilot pressure is applied to the pilot chamber 6 of the control valve 3, communication between the neutral passage 1 and the tank 8 is blocked to cause fluid in the neutral passage 1 to be supplied through the load check valve 10 to the arm cylinder.
When the control valve 2 is changed over to any position other than its neutral position in order to simultaneously actuate the boom cylinder while pressure fluid is supplied to the arm cylinder, the neutral passage 1 is closed to block supply of fluid to the control valve 3, so that supply of pressure fluid to the arm cylinder is blocked to lead to interruption of the arm cylinder. However, such interruption of actuation of the arm cylinder every time when the boom cylinder is moved prevents smooth work. In order to eliminate such a problem, the apparatus is adapted to supply fluid in the parallel passage 12 to the actuator passage 9. More particularly, keeping of the on-off valve 2 at its closed position shown in FIG. 1 causes the spool 13 of the change-over valve 11 to be also held at a normal position shown in FIG. 1, so that pressure fluid in the parallel passage 12 may be supplied through the first oil communication hole 17, communication hole 18, second oil communication hole 19 and load check valve 20 to the actuator passage 9. This results in supply of fluid in the parallel passage 12 to the arm cylinder being ensured even when the neutral passage 1 is closed.
When it is not needed to supply fluid in the parallel passage 12 to the arm cylinder, the on-off valve 22 is changed over to its open position. Such changing-over of the on-off valve 22 to the open position causes pressure loss in fluid passed through the orifice 21 to occur across the orifice, resulting in the balance of pressure between the spring 14 and the pilot chamber 15 to be lost. This causes the spool 13 to be moved against the spring 16, to thereby close the second oil communication hole 19.
Thus, the conventional control valve apparatus requires two spools or the spool for the control valve 3 and the spool for the change-over valve 11 separately, accordingly, it is required to form two spool holes in the valve, resulting in manufacturing of the apparatus being highly troublesome and its structure being significantly complicated. Also, this leads to large-sizing of the apparatus.